Multiple choice

Three pipes A, B and C can fill a cistern in 36 minutes after working together for 12 minutes C is closed and A and B fill the cistern in 48 minutes. Find the time in which the cistern can be filled by pipe C.

  1. 30 minute

  2. 48 minute

  3. 72 minute

  4. 45 minute

  5. 65 minute
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let total work = 1 unit. Combined rate of A+B+C = 1/36. In 12 minutes, they complete 12/36 = 1/3 of work. Remaining 2/3 is done by A+B in 48 minutes, so their combined rate = (2/3)/48 = 1/72. C's rate = 1/36 - 1/72 = 1/72. Therefore C alone takes 72 minutes.

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